This invention relates to a fluid flow control device. It may be used to control the flow of liquids or gases and may, for example, be used to provide velocity control of high pressure flowing fluids.
Devices of this general type are sometimes known as variable fluid restrictor control valves, and are exemplified by Self U.S. Pat. Nos. 3,451,404 and 3,514,074 which have frictional passageways, and by Self U.S. Pat. No. 3,513,864 which has multiple abrupt, angular turn passageways.
In the handling of flowing high pressure fluids, it has been customary to utilise orifice means having a high velocity short throat section to attain energy losses or high pressure drops. If the fluid is in a liquid state and liable to flash, that is, vaporise or turn to a gaseous condition on the downstream side of the orifice or valve opening, it may condense implosively and induce damaging shock waves, cause erosion, and the like. Also, as the velocity of the fluid in the valve exceeds the velocity of the fluid in the line, several disturbing reactions occur.
A most serious problem is rapid erosion of the valve surfaces by direct impingement of the liquid and any foreign particle suspended therein. Additional erosion results from cavitation. Cavitation may be defined as the high speed implosion of vapour against those internal parts of the valve controlling flow (the valve trim) and the valve body.
In addition to the severe problems resulting from erosion, the increased velocity also causes the flow characteristics of the valve to become unpredictable and erratic.
Other problems created by the high fluid velocity in the valve are severe noise generation, trim fatigue and possible degradation of flowing fluid materials such, for example, as polymers.
Fluid-borne noise downstream of control valves is often very high. If not treated or contained within the pipe, this noise can result in sound pressure levels of 110 to 170 dB about 0.9 m (three feet) from the valve exit. Sound sources of this magnitude are hazardous to personnel and frequently result in complaints from local residents.
Mufflers and silencers can typically only attenuate fluid-borne noise 20 to 30 dB. Therefore, only partial success has been achieved with them in obtaining desired sound pressure levels. Furthermore, a typical path treatment system i.e., the muffler, lagging support structure etc. is very cumbersome and expensive, often, the total cost of path treatment for noise can exceed the valve cost many times over.
In order to overcome or ameliorate the above problems, there have been introduced devices which effect energy losses in high pressure fluids without increasing velocity and shock wave reaction. This is achieved by subdividing the flow into a plurality of small, long passageways with abrupt turns creating friction and pressure drop in the fluid, thus avoiding damage and erosion in the equipment. Such a device is disclosed, for example, in U.S. Pat. No. Re 32,197.
There, the passageways are provided in an annular stack of separate members having abutting faces enclosing a plurality of individual passageway grooves. The grooves are angular between the inlet and outlet of the stack to turn the fluid and to provide a substantially longer flow length than between the inlet and outlet ends of the stack. The stack is mounted in the fluid passage of a valve housing and a valve plug movable within the annular structure controls the number of passageways in the stack through which the fluid can flow.
A modified device of this type is disclosed in GB-A-2,273,579 in which at least one passageway in the stack of members of discs includes a void between the inlet and outlet region of the disc, the void expanding the cross-sectional area of the energy loss passageway.
In our U.S. Pat. No. 5,687,763 we have described and claimed a structure having improved energy loss passageways, namely a fluid flow control device comprising a plurality of pairs of annular discs forming a rigid structure which incorporates a series of substantially radial passageways for fluid flow. Each disc of said pair has two major faces and passageways which extend completely through said disc between said major faces but extend only partially in a radial direction. The discs of each pair are substantially identical and are aligned with one another with a major face of one disc in direct abutment with a major face of the other disc. The passageways in said one disc interconnect with the passageways in the other disc of the pair so as to provide for fluid flow through the pair of substantially identical discs.
It is an object of the present invention to make a further improved flow control device and parts for use therein. It is also a preferred object of the present invention to provide a fluid control device in which erosion of surfaces, may be reduced.
Accordingly, in one aspect, the present invention provides a stack of annular discs for a flow control device, the discs forming a structure which incorporates a series of passageways for fluid flow, adjacent discs having abutting major surfaces to define said passageways therebetweeen, some at least of the discs each having a passageway extending from its outer perimeter to its inner perimeter, said passageway being formed of a depth to extend only partially into the thickness of the disc, a portion at least of the length of the passageway being curved, the curved portion of the passageway commencing at one of said perimeters and/or a portion at least of the length of the passageway being linear, the linear portion of said passageway commencing at the other of said perimeters.
Preferably, the passageways are grooves or channels formed in at least one of two major faces of a disc and being closed other than at their ends by an abutting major face of an adjacent disc.
In another aspect, the present invention provides an annular disc for incorporation in a fluid flow control device, which device comprises a stack of annular discs, the disc having an inner and an outer perimeter and at least one groove passageway formed in one of its major faces, a portion at least of the length of the passageway being curved, the curved portion of the passageway commencing at one of said perimeters and/or a portion at least of the length of the passageway being linear, the linear portion of the passageway commencing at the other of said perimeters.
The plurality of discs forms a stack in which central apertures of the discs define a central passageway for a reciprocatable plug. The fluid flow passageways formed by the discs lead into or lead from the central passageway depending on the direction of fluid flow through the stack. The plug is positionable in the central passageway to completely close off fluid flow at one extreme and to allow fluid flow through all the disc passageways at the other extreme. The position of the plug between these extremes may be adjusted to allow the desired flow rate between fully off and fully on, i.e. to allow flow through the passageways of a lesser or greater number of discs, as required.
In another aspect, the present invention provides a fluid flow control device incorporating a stack of annular discs, central apertures of the annular discs forming a central passageway extending longitudinally of the stack, a plug reciprocably movable within the central passageway and an actuator to move the plug as required to control fluid flow through the device from a fully closed through partially open positions to a fully open position, adjacent discs having abutting major faces defining at least one fluid passageway extending between inner and outer perimeters of the discs, said passageway being curved for at least a portion of its length commencing at one of said perimeters and/or being linear for at least a portion of its length commencing at the other of said perimeters.
In one embodiment, flow through the fluid passageways across the discs is from the outer perimeters to the inner perimeters of the discs, i.e. into the central passageway. The central passageway is then connected to an outlet for the fluid.
In another embodiment, flow through the fluid passageways across the discs is from the inner perimeters to the outer perimeters of the discs, i.e out of the central passageway. The central passageway is then connected to an inlet for the fluid.
In both embodiment, it is preferred that the fluid passageways have an initial linear portion commencing at an inlet end and then a curved portion across the disc terminating at an outlet end. Preferably, the linear portion is at an angle of less than 90xc2x0 to the tangent at the point of entry, i.e. at the junction of the passageway with the disc perimeter. For example, it may be at an angle of from 5xc2x0 to 30xc2x0 to that tangent.
When the fluid flows into the central passageway, it will enter that passageway at an angle to the radius at that point, erosion of the central passageway walls and of the valve plug thereby being reduced.
The passageways need not be of constant cross-section along their length and, indeed, it may be preferable that they increase or decrease in cross-sectional area between the inlet and outlet ends thereof. In order to maximise the energy loss imparted to a fluid travelling through the passageways or to allow for an increase in fluid volume that can occur with compressible media, it is particularly preferred that the passageways increase in cross-sectional area in the direction towards their outlet ends. Although such a cross-sectional area change may be achieved by varying the depth of the passageway at constant width, it is preferred to vary the passageway width at constant depth. Alternatively, the cross-sectional area may be changed by varying both the width and depth of the passageway.
A flow passageway with a continuously expanding area from the inlet end will see a significant flow capacity increase with erosion of the inlet. Accordingly, it may be advantageous to design the passageways with the initial linear portion of uniform cross-sectional area to keep the capacity of the passageway constant in that initial portion whereby the initial portion is more resistant to erosion.
A single disc may carry one or more passageways between its outer and inner perimeters. Thus, there may be, for example, one, two or three independent passageways across one major face of a disc.
A disc may have the fluid passageway(s) formed in one major face only with the other major face being planar for closing the passageway(s) of an adjacent disc. Alternatively, a disc may have fluid passageways formed in both major faces that are closed by abutting planar major faces of adjacent discs on each side.
When a disc and its passageway(s) are viewed in plan, the passageway(s) may extend in either a clockwise or a counter clockwise direction across the disc. Where a disc has more than one passageway, the passageways preferably extend in the same direction. For some applications, however, a combination of clockwise and counterclockwise passages may be found to be advantageous.
As indicated above, the preferred direction of fluid flow will be in the direction of increase of passageway cross-section. Reference to xe2x80x9cclockwisexe2x80x9d and xe2x80x9ccounter-clockwisexe2x80x9d passageways will herein, therefore, refer to the intended direction of fluid flow through those passageways.
In a preferred embodiment, the discs may be arranged so that clockwise passageways alternate in the stack of discs with counter clockwise passageways. This arrangement can permit flow disruptions that reduce or eliminate vortex production in the device outlet.
Alternatively, if desired, a vortex can be designed into the outlet by appropriate arrangement of the passageways. For example, the discs may be arranged with all the passageways extending in the same direction.
The discs may be flat but this is not essential and it may be found advantageous to utilise a stack of conical or dished discs. The dish effect of the disc imparts an axial vector to the process fluid as it discharges from or enters the disc and can further reduce the angle of impact at the plug throttling edge.
By way of example only, for an annular disc of about 4.75 inches overall diameter and about 1.12 inches radial extent from its inner to its outer perimeter, the linear portion of the passageway may extend for 0.5 to 2.0 inches and the curved portion of passageway for 1 to 4 inches on a variable radius of curvature of from 0.5 to 2.0 inches.
The discs may be made of any suitable material, depending on the valve requirements in which the fluid control device is to be used and, particularly, on the nature of the fluid and its temperature, pressure and velocity. The discs are preferably made of tungsten carbide or ceramic material.
The passageways may be formed across the discs by any convenient means and the skilled man of the art will readily be able to choose a suitable means depending on the chosen disc material. It is preferred to machine the passageways in discs made from tungsten carbide or from ceramic material in the green state before the disc has been fully hardened.
According to yet another aspect, the present invention provides a flow control device including a plurality of annular discs arranged in a stack, each disc having an outer perimeter and an inner perimeter, adjacent discs in the stack having opposed, abutting major surfaces providing at least one fluid passageway extending from the outer perimeter to the inner perimeter, the passageway having a linear portion commencing at one of the inner and outer perimeters and/or a curved portion commencing at the other of the inner and outer perimeters.
Preferably, the passageway is formed in a major surface of one disc and has a depth to extend only partially into the thickness of the disc, and the passageway is closed other than at its ends by the abutting major surface of the adjacent disc.
Advantageously, the linear portion is provided at an inlet end of the passageway and the curved portion is provided at an outlet end of the passageway. Preferably, the linear portion is of constant cross-section and the curved portion is of increasing cross-section in the direction of fluid flow. Advantageously, the linear portion extends at angle of less than 90xc2x0 to the tangent at the perimeter of the disc.
According to a still further aspect, the present invention provides an annular disc for a fluid control device comprising a stack of discs, the disc having an outer perimeter and an inner perimeter, the inner perimeter defining a central aperture, and the disc having at least one groove providing a fluid passageway in a major face on one side of the disc, the groove extending between the outer perimeter and the inner perimeter and having a linear portion at one end and/or a curved portion at the other end.
The linear portion may be provided at the inlet end of the fluid passageway, is preferably of constant cross-section and/or optionally extends at angle of less than 90xc2x0 to the tangent at the perimeter of the disc.
According to yet another aspect, the present invention provides a flow control device including a plurality of annular discs arranged in a stack, each disc having an outer perimeter and an inner perimeter, adjacent discs in the stack having opposed, abutting major surfaces providing at least one fluid passageway extending from the outer perimeter to the inner perimeter, wherein the discs are of conical shape.
By the use of discs having a conical shape, an axial vector is imparted to fluid flow through the passageway which may have advantages for certain applications.
Preferably, the passageway is formed in a major surface of one disc and has a depth to extend only partially into the thickness of the disc, and the passageway is closed other than at its ends by the abutting major surface of the adjacent disc.
Advantageously, a linear portion is provided at an inlet end of the passageway and a curved portion is provided at an outlet end of the passageway. Preferably, the linear portion is of constant cross-section and the curved portion is of increasing cross-section in the direction of fluid flow. Advantageously, the linear portion extends at angle of less than 90xc2x0 to the tangent at the perimeter of the disc.
According to a still further aspect, the present invention provides an annular disc for a fluid control device comprising a stack of discs, the disc being of conical shape having an outer perimeter and an inner perimeter, the inner perimeter defining a central aperture, and the disc having at least one groove providing a fluid passageway in a major face on one side of the disc, the groove extending between the outer perimeter and the inner perimeter and having a depth less than the thickness of the disc.
Preferably, the groove has a linear portion provided at the inlet end of the fluid passageway, and the linear portion may be of constant cross-section and/or optionally extends at angle of less than 90xc2x0 to the tangent at the perimeter of the disc.
According to a still further aspect, the present invention provides a flow control device including a plurality of annular discs arranged in a stack, each disc having an outer perimeter and an inner perimeter, adjacent discs in the stack having opposed, abutting major surfaces providing at least one fluid passageway extending from the outer perimeter to the inner perimeter, wherein the stack has discs with clockwise passageways alternating with counter clockwise passageways.
By the use of alternating clockwise and counter clockwise passageways, flow emerging from the passageways may be disrupted reducing or eliminating vortex production.
Preferably, the passageway between adjacent discs is formed in a major surface of one disc and has a depth to extend only partially into the thickness of the disc, and the passageway is closed other than at its ends by the abutting major surface of the adjacent disc.
Advantageously, a linear portion is provided at an inlet end of the passageway and a curved portion is provided at an outlet end of the passageway. Preferably, the linear portion is of constant cross-section and the curved portion is of increasing cross-section in the direction of fluid flow. Advantageously, the linear portion extends at angle of less than 90xc2x0 to the tangent at the perimeter of the disc.
Preferably, the passageway(s) of alternate discs are axially aligned at the inner perimeter and angularly offset at the inner perimeter relative to the passageway(s) of adjacent discs.
According to a still further aspect, the present invention provides an annular disc for a fluid control device comprising a stack of discs, the disc having an outer perimeter and an inner perimeter, the inner perimeter defining a central aperture, and the disc having at least one groove providing a fluid passageway in a major face on one side of the disc, the groove extending between the outer perimeter and the inner perimeter and having a linear portion of constant cross-section at an inlet end and a curved portion of increasing cross-section in the direction of fluid flow at an outlet end.
Preferably, the linear portion extends at angle of less than 90xc2x0, for example in the range 5xc2x0 to 30xc2x0 to the tangent at the perimeter of the disc, and the passageway extends in a clockwise or counter clockwise direction when the disc is viewed in plan.